The prevalence and characteristics of epilepsy in patients with multiple sclerosis in Nordland county, Norway

•The frequency of epilepsy is 4.5 times higher than in the general population.•MS with epilepsy has more likely converted to secondary progressive MS.•Epilepsy occurs after other signs of MS.•A high frequency of focal epilepsy among MS patients with epilepsy. The prevalence of epilepsy among patients with multiple sclerosis (MS) has been found higher than in the general population. Although cortical pathology may be involved, the causal link between MS and epileptic seizures is still unclear. We aimed to identify and describe the patients with active epilepsy in a previously described population based MS-cohort. Medical records of all patients with MS in Nordland County on January 1, 2010, were scrutinizing for evidence of comorbid seizures and epilepsy. Among 431 patients with MS, we identified 19 (4.4%) with a history of seizures or epilepsy. Fourteen (3.2%) of these had active epilepsy defined as use of antiepileptic drugs or seizures within the last 5 years. One patient got epilepsy before other signs of MS. In patients with relapsing-remitting MS (RRMS) at onset and active epilepsy (n=10), 70% had converted to secondary progressive (SPMS) at prevalence date, compared to only 35% of those without active epilepsy (p=0.02). 43% had converted to SPMS before they got epilepsy. Attack semiology or electroencephalogram recordings indicated a focal onset of seizures in 12 of 14 (86%) with active epilepsy. The frequency of active epilepsy among MS patients in Nordland was 3.2%, approximately 4.5 times higher than in the general Norwegian population. RRMS patients with active epilepsy had more likely converted to SPMS than patients without active epilepsy. With a high frequency of focal epilepsy, the study supports that focal MS brain pathology is the cause of the comorbid epilepsy.